Science fiction writers love the image of the "island galaxy" or "bubble galaxy" and build them into their stories. For example, in his classic 1937 short story Fessenden's Worlds, early science fiction great Edmond Hamilton paints a picture of a miniature universe:

It consisted of two twelve-foot metal disks with grid-like surfaces, one on the floor and one on the ceiling directly over the other...

Between the two disks, floating unsupported in the air, hung a cloud of tiny sparks of light. It looked like a swarm of minute golden bees, countless in number, and the swarm was lenticular in shape...

"Fessenden's eyes had been following my stupefied change of expression. He said calmly, "Yes, Bradley, it is true. That is a tiny, self-sustaining universe, with its own suns, nebulae and worlds. Everything in it, down to the atoms which compose it, is infinitely smaller in scale than our own. But it is a real universe, like our own."
(Read more about Hamilton's miniature universe)

Philip K. Dick had some fun with this idea in his 1953 short story The Trouble With Bubbles:

The Worldcraft bubble glittered, catching the light...

Lora turned on the bubble. It glowed, winking into brilliance...

She increased the magnification, bringing the microscopic central planet into focus...